Application Of Controlled-release Urea Research Articles

Integrated assessment of yield, nitrogen use efficiency and ecosystem economic benefits of use of controlled-release and common urea in ratoon rice production

Controlled-release urea (CRU) is commonly used to improve the crop yield and nitrogen use efficiency (NUE). However, few studies have investigated the effects of CRU in the ratoon rice system. Ratoon rice is the practice of obtaining a second harvest from tillers originating from the stubble of the previously harvested main crop. In this study, a 2-year field experiment using a randomized complete block design was conducted to determine the effects of CRU on the yield, NUE, and economic benefits of ratoon rice, including the main crop, to provide a theoretical basis for fertilization of ratoon rice. The experiment included four treatments: (i) no N fertilizer (CK); (ii) traditional practice with 5 applications of urea applied at different crop growth stages by surface broadcasting (FFP); (iii) one-time basal application of CRU (BF1); and (iv) one-time basal application of CRU combined with common urea (BF2). The BF1 and BF2 treatments significantly increased the main crop yield by 17.47 and 15.99% in 2019, and by 17.91 and 16.44% in 2020, respectively, compared with FFP treatment. The BF2 treatment achieved similar yield of the ratoon crop to the FFP treatment, whereas the BF1 treatment significantly increased the yield of the ratoon crop by 14.81% in 2019 and 12.21% in 2020 compared with the FFP treatment. The BF1 and BF2 treatments significantly improved the 2-year apparent N recovery efficiency, agronomic NUE, and partial factor productivity of applied N by 11.47–16.66, 27.31–44.49, and 9.23–15.60%, respectively, compared with FFP treatment. The BF1 and BF2 treatments reduced the chalky rice rate and chalkiness of main and ratoon crops relative to the FFP treatment. Furthermore, emergy analysis showed that the production efficiency of the BF treatments was higher than that of the FFP treatment. The BF treatments reduced labor input due to reduced fertilization times and improved the economic benefits of ratoon rice. Compared with the FFP treatment, the BF1 and BF2 treatments increased the net income by 14.21–16.87 and 23.76–25.96%, respectively. Overall, the one-time blending use of CRU and common urea should be encouraged to achieve high yield, high nitrogen use efficiency, and good quality of ratoon rice, which has low labor input and low apparent N loss.

Optimizing One-Time Nitrogen Fertilization for Rice Production Using Controlled-Release Urea and Urease Inhibitors

One-time fertilization with controlled-release urea (CRU) is a research hotspot for its lower labor cost and stability of nitrogen (N) supply for rice growth. Yet the fertilizer formulation needs to be further improved to better adjust the N supplement to meet the demand of rice plants and obtain a higher grain yield. Therefore, the effects of novel fertilizer formulations composed of CRU, urease inhibitor (UI) and nitrification inhibitor (NI) on the rice growth and photosynthetic characteristics as well as high-yield formation were tested through a two-year field experiment. The result indicated that the combined use of CRU and UI treatment can achieve higher yields than with CRU at the same N application level. Meanwhile, with a 20% reduction of N use, one-time application of CRU + UI can obtain the same high yield as the conventional split application of urea. Compared with conventional fertilization and CRU treatment, the CRU + UI treatment had suitable leaf area and biomass accumulation at the vegetative growth stage and high effective stem tiller rate. More post-anthesis dry matter accumulation, higher net photosynthesis rate and low senescence rate were guaranteed for its high yield and nitrogen agronomic efficiency.

Long-term application of controlled-release urea reduced ammonia volatilization, raising the risk of N2O emissions and improved summer maize yield

ContextWith the extensive promotion of controlled-release urea (CRU), its N-release pattern has been shown to match the crop’s N-demand period and improve crop yield by reducing N losses. Nevertheless, the impacts of CRU on summer maize yield, especially on greenhouse gas emissions, have rarely been reported during its long-term use. ObjectiveIt is necessary through long-term positioning field experiment with CRU application to investigate the regulatory mechanisms of maize yield formation, nitrogen use efficiency (NUE), ammonia volatilization and greenhouse gas emissions. MethodsThe long-term fertilizer positioning experiment for ten years, four treatments were performed: polymeric-coated controlled-release urea (CRF, 42% N, 3-months controlled-release period), sulfur-coated controlled-release urea (SCF, 35% N, 3-months controlled-release period), common urea (CCF, 46% N) and no nitrogen fertilizer (CK). ResultsResults showed that the two coated controlled-release fertilizers significantly increased NUE and dry matter accumulation in summer maize, and ultimately improved grain yield. Compared to CCF, CRF and SCF treatments increased post-silking dry matter accumulation by 16.3% and 13.3%; NUE by 42.3% and 28.9%. The 2-year mean grain yield of CRF and SCF treatment increased 9.0% and 12.4% compared to CCF treatment. CRF treatment significantly increased the NO3--N content in 0–60 cm soil layer; while CRF and SCF treatments showed a significantly higher NH4+-N concentration in the 0–20 cm soil layer than CCF treatment. Compared to CCF treatment, the CRF and SCF treatments significantly reduced peak ammonia volatilization, and the average cumulative emissions of ammonia volatilization of two years were reduced by 80.8% and 53.2%, respectively. CRF treatment had lower peak of N2O emissions but longer N2O emission duration than other N application treatments. The two-year average cumulative N2O emissions from CRF treatment increased by 49.6%, and SCF treatment increased by 61.1% compared to CCF treatment. Compared to CK treatment, total cumulative CH4 uptake was 36.1% lower in CRF treatment, 60.9% in SCF and 78.9% in CCF treatment. The higher cumulative N2O emissions from CRF and SCF treatment resulted in a significantly higher global warming potential (GWP) than CCF treatment. The two-year mean increase in greenhouse gas intensity (GHGI) was 36.2% for CRF treatment and 44.7% for SCF treatment compared to CCF treatment. ConclusionsLong-term application of coated controlled-release fertilizers could achieve high yields and nitrogen use efficiency. However, there is a risk of increased N2O emissions, causing elevated GHGI. SignificanceIn the future, it is necessary to strengthen the research on the comprehensive effects of long-term reduced application of CRU on crop yield and greenhouse gas emissions, in order to promote the wide application of environmentally friendly CRU in the field.

One-time application of controlled-release bulk blending fertilizer enhanced yield, quality and photosynthetic efficiency of late japonica rice

Controlled-release urea (CRU) releases nitrogen (N) at the same pace as rice uptakes N, which can effectively improve N use efficiency, increase rice yield and improve rice quality. However, few studies have described the effects of the application of CRU on the photosynthetic rate and endogenous enzyme activity of rice. Accordingly, a two-year field trial was conducted with a total of seven treatments (CK, no N fertilizer; BBF, regular blended fertilizer; RBBF, 20% N-reduced regular blended fertilizer; CRF1, 70% CRU+30% regular urea one-time base application; CRF2, 60% CRU+40% regular urea one-time base application; RCRF1, CRF1 treatment with 20% N reduction; RCRF2, CRF2 treatment with 20% N reduction). Each treatment was conducted in triplicate. The results showed that the N recovery efficiency (NRE) of the controlled-release bulk blending fertilizer (CRBBF) treatments was significantly increased over the two years. There were significant yield increases of 4.1–5.9% under the CRF1 treatment and 5.6–7.6% under the CRF2 treatment compared to the BBF treatment, but the differences between the reduced N treatments RBBF and RCRF2 were not significant. The photosynthetic rates under the CRF1 and CRF2 treatments were significantly higher than under the other treatments, as well as significantly increased RuBPCase, RuBisCO, GOGAT and GS enzyme activity. Additionally, the soil NH4+-N and NO3−-N content under the CRBBF treatments was significantly higher at the late growth stage of rice, which was more in line with the fertilizer requirements of rice throughout the reproductive period. The CRBBF also led to some improvement in rice quality. Compared with the BBF and RBBF treatments, the protein content under the CRBBF treatments was reduced but the milling, appearance, eating and cooking quality of the rice were improved. These results showed that the application of CRBBF could improve the NRE, photosynthetic rate and endogenous enzyme activity of rice, ensuring sufficient N nutrition and photosynthetic material production during rice growth and thereby achieving improved rice yield and quality.

Optimization of controlled-release urea application based on the winter wheat yield

Wheat is of great significance to ensuring national food security in China. The one-time fertilization for saving labor was common in winter wheat production in the North China Plain, which caused the excessive application of nitrogen (N) fertilizer generally. Controlled-release urea (CRU) has a good application effect in crops with short growth periods such as rice and maize. However, the applications of CRU on winter wheat with a longer growth period are fewer. To investigate the appropriate dosage and blending proportion of CRU and urea in wheat production, the field experiment with 52 treatments was conducted in 2019–2021. This relationship among N application rates, CRU release longevity, CRU proportions and winter wheat yield was systematically studied, and the binary quadratic effect models between yield and CRU factors were established. N application rates, CRU proportion and the interacted effect of CRU proportion and release longevity had the greatest effect on winter wheat yield by the main effects test and correlation analysis. The winter wheat yield could be accurately predicted by CRU proportions and CRU release longevity. The prediction errors of yield models were −9.8%∼4.9% based on the 2018 and 2022 two years winter wheat yield with CRUs application. Reducing N application rates by 20∼30% and mixing with appropriate CRU proportion would increase the yield and NUEs (nitrogen use efficiencies) of winter wheat. In the case of low CRU proportion, the wheat yield could be increased by applying the CRU with long-release longevity; when the CRU proportion was high, the yield increase effect of the CRU with short-release longevity was better. Comprehensive field production survey and Response surface methodology (RSM) partial derivative analysis, CRUs with controlled release longevity of 57d∼150d and CRU proportion of 24∼64% were the best choices for increasing wheat yield and reducing N application rates. It will facilitate the optimization of wheat CRU manufacture and application and promote the ‘Reduction and Efficiency of Chemical Fertilizers’ policies and environmental protection.

Assessment of the crucial factors influencing the responses of ammonia and nitrous oxide emissions to controlled release nitrogen fertilizer: A meta-analysis

Reducing ammonia (NH3) and nitrous oxide (N2O) emissions have great effects on mitigating nitrogen (N) nutrient loss and greenhouse gas emissions. Controlled release urea (CRU) can control the N release rate, which reduces reactive N loss and increases nitrogen use efficiency relative to conventional urea (CU). However, the crucial factors influencing the responses of NH3 and N2O emissions to CRU relative to CU are still unclear. In this study, we evaluated the responses of NH3 and N2O emissions to CRU based on collected field data with a meta-analysis. CRU reduced the NH3 and N2O emissions by 32.7 and 25.0% compared with CU, respectively. According to subgroup analysis, CRU presented better mitigation of NH3 and N2O emissions in soils with pH 6.5–7.5 (–47.9 and –23.7%) relative to either pH<6.5 (–28.5 and –21.4%) or pH>7.5 (–29.3 and –17.3%), and in the rice season (–34.8 and –29.1%) relative to the wheat season (–19.8 and –22.8%). The responses of NH3 and N2O emissions to CRU increased from rainfed (–30.5 and –17.0%) to irrigated (–32.5 and –22.9%), and then to paddy (–34.8 and –29.1%) systems. In addition, the response of N2O emission mitigation increased with increases in soil total nitrogen (TN); however, soil TN did not significantly affect the response of NH3 volatilization. The reduction in NH3 emission was greater in sandy-textured soil (–57.7%) relative to loam-textured (–32.9%) and clay-textured (–32.3%) soils, whereas soil texture did not affect N2O emission. Overall, CRU was a good option for reducing the NH3 and N2O emissions relative to CU in agricultural production. This analysis improves our understanding of the crucial environmental and management factors influencing the mitigation of NH3 and N2O emissions under CRU application, and these site-specific factors should be considered when applying CRU to reduce reactive N loss and increase NUE.

Controlled-release urea application and optimized nitrogen applied strategy reduced nitrogen leaching and maintained grain yield of paddy fields in Northwest China.

Nitrogen loss from paddy fields contributes to most of the nitrogen pollution load in the Ningxia Yellow River irrigation area, threatening the water quality of the Yellow River. Consequently, optimizing the nitrogen management practices in this area is essential, which can maintain paddy grain productivity and reduce nitrogen loss simultaneously. Five treatments with different nitrogen application rates and nitrogen fertilizer types were set in this study, including conventional urea application with zero nitrogen application rate (CK, 0kg hm-2), nitrogen expert-based fertilization application strategy (NE, 210kg hm-2), optimized nitrogen fertilizer application strategy recommended by local government (OPT, 240kg hm-2), and farmer's experience-based nitrogen fertilizer application strategy (FP, 300kg hm-2), and controlled-release urea application (CRU, 180kg hm-2). The data from one growth season field experiment in 2021 revealed the dynamics of nitrogen concentration, paddy yield and its nitrogen uptake characteristic, and nitrogen balance in the paddy field under different nitrogen application practices. Most nitrogen leaching was observed during the seedling and tillering stages in the form of nitrate nitrogen (NO3 -N). Compared with the FP, the CRU and OPT significantly reduced the nitrogen concentrations of total nitrogen (TN), ammonium nitrogen (NH4 +-N), and NO3 -N in the surface and soil water and reduced the nitrogen leaching at 100cm soil depth. Meanwhile, the paddy grain yield in CRU (7737kg hm-2) and OPT (7379kg hm-2) was not significantly decreased compared with FP (7918kg hm-2), even though the nitrogen uptake by grain and straw was higher in FP (135kg hm-2) than in other treatments (52.10~126.40 kg hm-2). However, the grain yield in NE (6972kg hm-2) was decreased compared with the FP. The differences in grain yield among these treatments were mainly attributed to the ear number and grain number changes. Also, the highest nitrogen use efficiency (40.14%), apparent nitrogen efficiency (19.53kg kg-1), and nitrogen partial productivity (43.98kg kg-1) were identified in CRU than in other treatments. Considering increased grain yield and reducing nitrogen loss in the paddy field simultaneously, the treatments of CRU (i.e., 180kg hm-2 nitrogen application rate with controlled-release urea) and OPT (i.e., 240kg hm-2 nitrogen application rate with conventional urea) were recommended for nitrogen fertilizer application in the study area.

Combining Controlled-Release Urea and Normal Urea to Improve the Yield, Nitrogen Use Efficiency, and Grain Quality of Single Season Late japonica Rice

Controlled-release urea (CRU) is widely adopted to improve yields and nitrogen use efficiencies (NUEs) in rice. However, there are few studies on the effects of the mixed application of CRU and normal urea (at different N ratios) on rice yield, nitrogen efficiency, and grain quality. A series of simplified fertilization modes (SFMs) were set up in 2018–2019. CRU with release periods of 80 days and 120 days were mixed with urea at N ratios of 7:3, 6:4, 5:5, 4:6, and 3:7 and applied during the rice-growing season. We determined the rice yield, dry matter accumulation, NUEs, and grain quality. The yields of SFM_80_6/4 (CRU with release periods of 80 days were mixed with urea at N ratios of 6:4) and SFM_120_5/5 (CRU with release periods of 120 days were mixed with urea at N ratios of 5:5) were 3.69% and 4.39% higher than that of fractionated urea (FU), respectively, across 2018 and 2019. Combining the application of controlled-release urea and normal urea improved the dry matter accumulation, nitrogen accumulation, and nitrogen uptake rate when compared with FU. SFMs improved the processing quality and appearance quality of rice grains and did not reduce the cooking and eating quality. SFM_80_6/4 and SFM_120_5/5 are a one-time fertilization mode with high yield, high efficiency, and good grain quality, which is worthy of further promotion and application.

Increase in yield and nitrogen use efficiency of double rice with long-term application of controlled-release urea

Controlled-release urea (CRU) has better characteristics than conventional urea for synchronizing nitrogen (N) release with plant uptake. Understanding the effects of CRU on crop yield and N use efficiency (NUE) has long been the key to evaluate the performance of CRU. A long-term experiment over five consecutive years was conducted in Changsha, Hunan Province, China, to investigate the effects of polyethylene-coated urea with a 90-d release period on the yield and NUE of double rice (early and late crops are grown in the same year), the amount of residual soil mineral N and the soil–plant N balance, as well as on the economic benefits. Four N fertilizer treatments including CK (no N fertilizer), U (conventional urea), CRU1 (polyethylene-coated urea with equal N application rate to U) and CRU2 (20% reduction in N application rate of CRU1) were established. The results indicated that CRU1 application increased the yield and NUE of double rice by 11.0 and 13.5%, respectively, compared with U. Higher yield and NUE of late rice were found than in early rice in CRU treatments. Compared with conventional U, the yield and NUE of early rice in the CRU1 treatment were increased by 6.0 and 10.2%, respectively, and those of late rice were increased by 15.4 and 13.8%, respectively. There was no significant difference between CRU1 and CRU2 in double rice yield. Furthermore, CRU treatments (including CRU1 and CRU2) had higher apparent residual Nmin rate (ARNR) and apparent N recovery rate (ANRR), but lower apparent N loss (NS) than the conventional U treatment. Concentrations of NH4+-N and NO3–-N were greater in the surface soil (0–20 cm) and lower in the deeper soil layer (40–60 cm) with CRU treatments than in the U treatment after harvest. Moreover, CRU application produced a greater economic benefit than conventional U application. In general, CRU outperformed U fertilizer in terms of rice yield, NUE, soil–plant N balance, economic benefit, and CRU2 provided greater comprehensive benefits than CRU1. It is suggested that CRU application is beneficial for solving N management challenges in the production of rice.

Combined effects of urea type and placement depth on grain yield, water productivity and nitrogen use efficiency of rain-fed spring maize in northern China

Inappropriate nitrogen (N) application can lower N use efficiency (NUE) and crop water productivity (WP), and further affect the sustainable development of agriculture in the rain-fed areas of northern China. It is thus crucial to improve NUE and WP by developing a suitable nitrogen fertilization strategy. In this study, two urea types (UT), i.e., conventional urea (CU) and controlled-release urea (CRU), and three urea placement depths (PD) including 8 cm (D8), 16 cm (D16) and 24 cm (D24) were tested on rain-fed spring maize in 2017, 2018 and 2019. Grain yield (GY), partial factor productivity of N (PFPN), WP and nitrate N residue (NR) were evaluated. Compared with D8, D16 and D24 enhanced evapotranspiration, dry matter and N uptake of spring maize, and the increases were greater under CRU than CU. D16 produced the highest GY and WP among the placement depths, with mean values of 8417.8 kg ha−1 and 21.4 kg ha−1 mm−1, respectively. Compared with CU, CRU obtained higher mean GY (8754.5 vs. 7554.6 kg ha−1) and WP (21.8 vs. 20.2 kg ha−1 mm−1). The effects of UT × year and PD × year interactions on GY and WP were significant, indicating that these indicators had various responses to the planting year. The effects of UT × PD interaction on GY, WP and PFPN were not significant, suggesting that these indicators had similar responses to PD, independent of CRU or CU. CRU increased NR in the 0–80 cm soil profile, whereas it lowered NR in the 80–120 cm soil profile at harvest. Overall, the application of controlled-release urea at a placement depth of 16 cm achieved a better balance between agronomic and environmental benefits of rain-fed spring maize in northern China.

Use of Controlled-Release Urea to Improve Yield, Nitrogen Utilization, and Economic Return and Reduce Nitrogen Loss in Wheat-Maize Crop Rotations

Excessive nitrogen (N) fertilizer input has become a common phenomenon among most farmers in the winter wheat–summer maize rotation system of north-central China, and has resulted in low nutrient use efficiency and environmental pollution. Controlled-release urea (CRU) is proposed as a solution to excessive fertilization because CRU achieves high yields and reduces N losses. Therefore, CRU mixed with normal urea at rates based on the Nutrient Expert (NE) system was used as fertilizer in a 4-year field experiment to test the preference in crop yields, economic benefits, nitrogen use efficiencies, and N losses. The following fertilizer treatments were established: local farmers’ practices (FP); normal urea fertilizer at the rate recommended by the NE system (NE); mixed CRU and normal urea at ratios of 60:40 (CRU1) and 75:25 (CRU2) based on the NE system; and 80% of the recommended N rate of the NE, CRU1 and CRU2 treatments (80%NE, 80%CRU1 and 80%CRU2). The results showed that, compared with the NE treatment at the same application rate of N, mixed CRU and urea increased yields and net benefits while reducing N loss. The application of CRU at 60% for maize and 75% for wheat had the best overall effects. Compared with FP, the average grain yield, recovery efficiency of N fertilizer and net benefits increased by 8.5%, 10.9% and 11.3%, respectively, for maize with CRU1, and increased by 4.5%, 15.1% and 10.3%, respectively, for wheat with CRU2. Furthermore, mixed CRU and urea at the recommended N rate significantly reduced N loss from 38.5% to 40.3% but increased soil NO3−-N and NH4+-N contents at 0–30 cm, although opposite results (NO3−-N) were observed deeper in the soil (30–90 cm). In the treatments 80%CRU1 and 80%CRU2, the maize yield and overall economic benefits were equivalent to those in the FP treatment, but apparent N loss was significantly reduced. Thus, these results confirmed that the combination of the CRU and the NE system for winter wheat–summer maize in north-central China is efficient and valuable, and has the potential to improve yield, nitrogen use efficiency and net benefit with low N losses.

Effects of Fertilization on Yield and Nitrogen Use Efficiency of Wheat and Rice with Straw Return

ABSTRACT Fertilizer application of controlled-release urea (CRU) is a feasible fertilization method because of its simple operation, high efficiency, environmental friendliness, and labor-saving. However, the high cost of CRU and the dynamic change of nitrogen (N) demand caused by straw return make it necessary to find a better fertilization method. Therefore, we investigated the effects of application of the mixed CRU and urea on the yield and nitrogen use efficiency (NUE) of wheat and rice, and soil fertility with straw return. The results indicated that application of the mixed CRU and urea increased the yield of wheat and rice compared with 100% urea application. The maximum increments of yield of wheat and rice occurred in the substitution ratio of CRU with 50%. Reducing N application rate of the mixed CRU and urea in wheat by 20% and rice by 15% also increased the yield of wheat and rice compared with 100% urea. Applying the mixed CRU and urea increased NUE of wheat and rice, compared with 100% urea. The maximum increments of NUE of wheat and rice were 31.9% and 37.4%, respectively. Reducing N application rate of the mixed CRU and urea could further increase NUE of wheat and rice. Compared with 100% urea, applying the mixed CRU and urea increased soil organic carbon, total N, alkaline N, and urease concentration. In summary, application of the mixed CRU and urea is feasible to achieve stable crop yield and to improve NUE with straw return. In addition, the application of CRU requires less N fertilizer application. Therefore, application of mixed CRU and urea is of great significance to ensure national food security and sustainable agricultural development.

Co-application of controlled-release urea and a superabsorbent polymer to improve nitrogen and water use in maize

ABSTRACT A field experiment consisted of two types of N fertilizer, controlled release urea (CRU) and normal urea (U), in combination with three SAP application rates (0, 45 and 90 kg ha−1) in a split-plot design was conducted in 2018 and 2019. The successive release of N from polymer-coated urea corresponded well to the N requirements of maize growth. The NO3 −-N and NH4 +-N contents in the 0–20 cm soil layer were enhanced at the jointing and 12 leaf collar stages, and the leaching of soil NO3 −-N was reduced by using CRU. The application of superabsorbent polymer (SAP) increased soil water stock, decreased evapotranspiration, and enhanced water use efficiency (WUE) and nitrogen use efficiency (NUE). The combined application of CRU and 90 kg ha−1 SAP achieved maximal maize yield, WUE, NUE, and net income values that were 0.8–32.9%, 0.2–37.4%, 4.1–13.1%, and 2.8–42.1%, respectively, higher than those of other treatments. These results demonstrate that the co-application of CRU and 90 kg ha−1 SAP is an effective practice that enhances the water and N utilization of maize and could potentially have wide application on the North China Plain.

Application of controlled release urea improved grain yield and nitrogen use efficiency: A meta-analysis.

The application of controlled release urea (CRU) has been proposed as a crucial method to reduce the adverse environmental effects induced by conventional urea (CU). Yet, a systematic and quantitative analysis on how CRU affects staple crop production including wheat (Triticum aestivum L.), maize (Zea mays L.), and rice (Oryza sativa L.) is lacking. Here, a meta-analysis was conducted to determine how CRU influences soil chemical properties, total nitrogen (TN) uptake, grain yield, and nitrogen use efficiency (NUE) of staple crop in China. The results indicated that CRU application significantly increased soil organic carbon (SOC), TN, and available nitrogen (AN) by 5.93%, 3.89% and 13.98% respectively overall, while soil pH showed no significant changes. Compared to the application of CU, applying CRU significantly increased grain yield by 7.23%, which was mainly owing to the higher TN uptake (9.13%) across all the studies. In addition, the application of CRU significantly increased NUE, nitrogen agronomy efficiency (NAE), utilization rate of nitrogen fertilizer (NUR), and nitrogen physiological efficiency (NPE) by an average of 23.4%, 34.65%, 25.83% and 15.8% respectively which could be attributed to the slow nitrogen (N) release characteristics of CRU. The positive effect of CRU on grain yield and NUE of staple crop was greatest when the content of SOC and TN were extremely low, indicating that it was most effective to improve grain production of infertile soil by applying CRU. The finding of this study indicated that the application of CRU should be promoted for grain production, especially for infertile soil.

Effects of controlled-release urea combined with fulvic acid on soil inorganic nitrogen, leaf senescence and yield of cotton

A split-plot field experiment was conducted in 2018–2019 to study the effects of nitrogen fertilizer types and fulvic acid (FA) rates on soil nitrogen and cotton growth. The nitrogen fertilizers included controlled-release urea (CRU) and urea, which were applied combined with three FA rates (90, 180 and 270 kg ha-1). The main plot was the nitrogen fertilizer type, and the subplot was the FA rate. The results showed that the lint yield of the FA180 treatment was 5.2–8.6% higher than the FA90 and FA270 treatments. Moreover, moderate FA application markedly improved the cotton leaf SPAD value (chlorophyll relative value), photosynthesis and chlorophyll fluorescence parameters compared with low and high FA rates. Replacing urea with CRU significantly increased the soil inorganic nitrogen and nitrogen use efficiency and also improved cotton fiber quality parameters. Meanwhile, the boll weight and seed yield of the CRU treatments were 1.5–8.4% and 3.3–19.1% higher, respectively, than the urea treatments. The interaction between nitrogen type and FA rate had a positive effect on cotton growth. Thus, the application of CRU combined with 180 kg ha-1 FA on cotton can not only improve the fiber quality and delay leaf senescence but also increase the yield and economic benefit.

Impact of controlled-release urea on rice yield, nitrogen use efficiency and soil fertility in a single rice cropping system

Overuse of nitrogen (N) fertilizer has led to low N use efficiency (NUE) and high N loss in single rice cropping systems in southeast China. Application of controlled-release urea (CRU) is considered as an effective N fertilizer practice for improving crop yields and NUE. Here, field experiments were conducted during 2015–2017 to assess the effects of two CRUs (resin-coated urea (RCU) and polyurethane-coated urea (PCU)) on rice yields, NUE and soil fertility at two sites (Lincheng town (LC) and Xintang town (XT)). Four treatments were established at each site: (1) control with no N application (CK), (2) split application of conventional urea (U, 270 kg N ha−1), (3) single basal application of RCU (RCU, 216 kg N ha−1), and (4) single basal application of PCU (PCU, 216 kg N ha−1). The N application rate in the CRU treatment compared to the U treatment was reduced by 20%. However, the results showed that, compared to split application of urea, single basal application of CRU led to similar rice grain yields and aboveground biomass at both sites. No significant difference in the N uptake by rice plant was observed between the U and CRU treatments at either site. There were no significant differences in the N apparent recovery efficiency (NARE) among the U, RCU and PCU treatments, with the exception of that in XT in 2015. Compared to application of U, application of CRU increased the N agronomic efficiency (NAE) and N partial factor productivity (NPFP) by 17.4–52.6% and 23.4–29.8% at the LC site, and 15.0–84.1% and 23.2–33.4% at the XT site, respectively, during 2015–2017. Yield component analysis revealed that greater rice grain yield in response to N fertilizer was attributed mainly to the number of panicles per m2, which increased in the fertilized treatments compared to the CK treatment. The application of CRU did not affect the soil fertility after rice harvest in 2016. Overall, these results suggest that single basal application of CRU constitutes a promising alternative N management practice for reducing N application rates, time- and labor-consuming in rice production in southeast China.

Effect of controlled-release urea fertilizers for oilseed rape (Brassica napus L.) on soil carbon storage and CO2 emission.

Fertilizer-induced CO2 emission is a primary driver of global warming. The experiment was used to study whether controlled-release urea (CRU) application in winter oilseed rape can play a positive role in mitigating CO2 emission and promoting C utilization by soil microorganisms. Five fertilizer types consisted of N0 (0 g N plant-1), conventional CRU application (CRU100%), monotypic CRU at the 80% of conventional rate (CRU80%), co-application of CRU with uncoated urea (CRC), and organic fertilizer (CRO). Results showed that soil CO2 fluxes were significantly affected by N fertilizer types after the start of the stem growing (P < 0.05). CO2 emissions typically peaked during the seed filling period, with the highest emission of 1.99 μmol m-2 s-1 being registered for CRU100%. CRU100% had 25.00%, 30.60%, and 4.17% greater CO2 emissions than CRU80%, CRC, and CRO practices by harvest, respectively. Compared to the conventional CRU treatment, CRU80% led to a lower root volume and root mass ratio than CRU100%, which could partly contribute to the reduced CO2 emission. Conversely, CRU80% performed better in N agronomic efficiency than that of CRU100% treatment. Also, C source utilization by soil microbiomes as well as microbial diversity indices following CRU80% along with CRO applications was substantially higher than that under the conventional CRU supply. These observations suggest that opportunity exists to maintain N balance by N fertilization practices to mitigate CO2 emission from cropland. Further, a close and positive relationship between soil total nitrogen and CO2 emission also supports this. CRO-treated soils substantially elevated the contents of total carbon and readily oxidation carbon over CK. Moreover, the enzyme activity of β-glucosidase in CRO soil was about twice as high as the CRU100%. Consequently, CRU amendments by decreasing CRU rate application and the incorporation of organic fertilizer into CRU have the potential for mitigating of CO2 emission and positive effect on the soil microbial functional diversity to improve nitrogen use efficiency of rapeseed.

Paecilomyces variotii Extracts and Controlled-Release Urea Synergistically Increased Nitrogen Use Efficiency and Rice Yield.

A novel biostimulant, Paecilomyces variotii extracts (ZNC), with the ability to promote N absorption in the plant at a very low level has been proved in the lab experiment, but its chemical composition and practical effect in the field remain unclear. In this work, we determined the molecular composition of ZNC. Then, a three-year field experiment was conducted to investigate the synergistic effects of controlled-release urea (CRU) without ZNC or with ZNC at three doses (87.5, 175, and 262.5 mL ha–1) on the yield, nitrogen use efficiency (NUE), and net returns of rice. Results indicated that ZNC contained more carbohydrates, amino acids, alkyl structures, and less aromatic structures with a molecular weight between 140 and 2507 Da. Rice yield was 6.9–21.0% higher with CRU than with conventional urea. Combining CRU with ZNC at a dose of 87.5 mL ha–1 performed the best and significantly increased rice yields by 8.7–12.1%, NUE by 15.0–20.2%, and average net returns by 10.9–15.4% during three rice-growing seasons compared to the application of CRU only, which is attributed to the positively increasing panicles and N uptake of rice. With the increased dose of ZNC, the yield of rice showed a decreasing trend, but the yield was still higher/not significant than the CFF treatment without ZNC. Therefore, the planting patterns with the combination of CRU and biostimulant are an efficient way to increase the rice grain yield and net returns.

Reduced N Fertilizer Application with Optimal Blend of Controlled-Release Urea and Urea Improves Tomato Yield and Quality in Greenhouse Production System

At present, excessive nitrogen (N) fertilizer application for tomato has attracted much research attention because of reducing fruit yield and quality and increasing fertilizer input cost and environmental pollution risks. A better management strategy of controlled-release urea (CRU) combined with normal urea for reducing the N application rate and maximizing tomato yield has led to the feasibility of their adoption in many cropping systems. The interactive effects of three blending ratios of urea to controlled-release urea (CRU) (6:4, 3:7, 0:10) and three levels of N fertilizer application rate (reduction by 15%, 30%, and 45% compared with conventional fertilization rate) on tomato yield and quality, economic return, nitrogen use efficiency (NUE), and soil inorganic N contents were investigated in greenhouse production system. The results indicated that application of CRU significantly increased tomato yield and NUE by 1.7–20.1% and 7.7–26.5%, respectively, compared with that of conventional fertilization (CF) treatment. Meanwhile, proper proportion of CRU and urea significantly improved tomato fruit Vitamin C concentration and sugar-acid ratio, which were 12.6–22.4% and 12.4–22.6% higher than that in the other N fertilizer treatments, respectively. The highest tomato yield and quality were achieved with the 15% reduction in N fertilization rate with urea to CRU blending ratio of 3:7, suggesting that the conventional N application rate exceeded what tomato requires. The study identified that a 15% reduction in N fertilization rate with urea to CRU blending ratio of 3:7 rendered a sustained supply of inorganic N in topsoil and optimal NUE during the growing season. This finding had practical implications for developing a sustainable N fertilization strategy, which reduced N fertilizer application with optimal blending of CRU with urea while maintaining high yield and quality for large-scale application in tomato production under greenhouse system.

Deep placement of controlled-release urea effectively enhanced nitrogen use efficiency and fresh ear yield of sweet corn in fluvo-aquic soil

Application of controlled-release urea (CRU) improves crop yield and nitrogen use efficiency (NUE) compared with conventional urea. However, the effectiveness of CRU differs with fertilization placement. A two site-year field experiment was carried out in fluvo-aquic soil in central China to study the effects of two N sources (CRU and urea) and three fertilization placements (band application between two corn rows at 0, 5, and 15 cm soil depths) on fresh ear yield and NUE of sweet corn. The soil inorganic N (NO3−-N and NH4+-N) concentrations at the soil layers of 0–20 cm and 20–40 cm, root morphology characteristics and leaf physiological functions were also measured during the sweet corn growth period. Results showed that the deep placement of CRU at 15 cm soil depth significantly increased the sweet corn fresh ear yield, total N uptake, and NUE by 6.3%–13.4%, 27.9%–39.5%, and 82.9%–140.1%, respectively compared with CRU application at 0 cm depth. Deep placement of CRU at 15 cm also increased the root morphology traits, gas exchange attributes, and soil NO3−-N and NH4+-N concentrations in 0–20 cm and 20–40 cm layer, especially during later crop growth stages. However, the different N placements exerted non-significant effects on NUE and fresh ear yield when urea was applied as the N source. In crux, deep CRU placement instead of urea at 15 cm depth can effectively improve fresh ear yield and NUE of sweet corn in fluvo-aquic soil because of higher root growth, better leaf physiological functions and increased availability of soil NO3−-N and NH4+-N.